The now-permanently closed San Onofre nuclear power plant in southern California had been offline since Jan. 2013. New power sources, including renewable energy, have come online. The power is there, even if the bulk of it is from natural gas. However, since the electricity is no longer generated locally, the transmission grid will need to be upgraded to handle it reliably.

This new capacity will help make up for the loss of the generation from SONGS, but the reliability issue is more complicated than simply providing replacement generation. Geographically, SONGS is in a localized pocket of electric power demand near San Diego and Los Angeles. Given the characteristics of the electric transmission system, the loss of SONGS limits the amount of power that can be brought into the area over the transmission grid—rather than generated locally—under some conditions.

The chart is a little misleading. California gets large amounts of power from out of state, primarily from hydro in Washington and Nevada and well as from their dirty little secret, coal power in Arizona and Utah. The City of Los Angeles in particular still gets substantial amounts of power from coal plants on Indian land in Arizona.